The invention relates to an apparatus and a process for carrying out reactions in fluidized particle beds, reactants being blown into the fluidized particle beds.
Reactions in fluidized particle beds are known, where these beds can be stationary beds in fluidized-bed reactors or streams of particles suspended in gas in reactors having a circulating fluidized bed, in which the particle stream discharged from the reactor is completely or partly separated from the gas stream and recirculated to the lower region of the reactor. The fluidized particles can be not only reactants, such as in roasting processes, coal combustion, chlorination processes etc. but also catalysts, such as in cracking processes, hydrogenation reactions etc., or inert material. In the multiplicity of the reactions carried out on an industrial scale in fluidized particle beds (FPB), in which the fluidizing medium is gaseous, the gas distributor plates through which the fluidizing gases are passed into the reactors frequently pose a problem, because they are exposed to both chemical and engineering effects. A further problem arises in the case of large reactors owing to the fact that the uniform gas distribution over large gas distributor plates is difficult and that high demands are made of the mechanical load-bearing capacity of the gas distributor plates on shutdown of operations. Finally, in the case of lateral particle feed, inadequate radial particle mixing can lead to zones having different reaction conditions within the FPB.
Particular problems with carrying out reactions in FPBs arise when two or more gaseous or liquid reactants are to be passed separately into an FPB, because, for example, they form explosive mixtures on mixing outside the FPB. If one or more of these reactants is passed through orifices in the reactor wall, problems arise owing to uneven distribution of the different reactants in the FPB. In order to avoid this, complicated apparatuses are used in which the various reactants are introduced through the gas distributor plates via separate feed lines.
The use of oxygen in stationary or circulating fluidized-bed reactors is known in the case of oxidizing reactions, such as, for example, the roasting of sulfidic ores, the thermal cleavage of waste sulfuric acids, the calcination of clay or the combustion of sewage sludges. By using air as fluidizing gas, the solid particles are fluidized, which means they are held in suspension, and simultaneously oxygen is fed together with the reactants for the oxidizing reactions. Fluidized particles can be oxidizable reactants, inert substances or catalysts.
In addition, it is known to increase the capacity of apparatuses and, in the case of exothermic reactions, such as the cleavage of waste sulfuric acid, to reduce the fuel requirement, by using oxygen or oxygen-enriched air instead of combustion air. If the fuels are burnt using burners (DE 2 506 438), this procedure is unproblematic. The use of oxygen-enriched air also brings advantages when such reactions are carried out in fluidized-bed reactors (DE 3 328 708). However, in this case, relatively narrow limits are set for the oxygen content, on the one hand owing to the resistance of the materials in the region of the feed system for the fluidizing air and, on the other hand, by a temperature elevation in the immediate vicinity of the gas distributor plate owing to the oxygen enrichment. These lead to problems with regard to the mechanical strength and scaling of the plates.
It was therefore an object of the present invention to provide an apparatus and a process for carrying out reactions in fluidized particle beds using which the abovementioned problems, such as uneven distribution in the FPB, chemical and mechanical strength and load-bearing capacity of the gas distributor plates, uneven gas distribution and inadequate radial particle mixing and differing reaction conditions in the FPB can be avoided and using which operations can be carried out effectively and inexpensively.
This object was achieved by the reactor according to the invention and the process according to the invention.
Surprisingly, it has been found that the above-mentioned problems can be substantially or completely solved by transversal injection of reactants into the FPB at supersonic speed.
The invention relates to a reactor having a gas distributor plate through which a fluidizing gas is introduced into a particle bed situated above this gas distributor plate to produce a fluidized particle bed, in which one or more supersonic nozzles are arranged in the reactor wall above the gas distributor plate.
The reactors are reactors in which, by feeding fluidizing gas through a gas distributor plate, a fluidized particle bed is formed above this plate and in which reactants are injected into this fluidized particle bed at supersonic speed through transversal supersonic nozzles radially or at an angle to the radius.
The supersonic nozzles, also known as Laval nozzles, are, if required, preferably provided with a cooling jacket.
Supersonic nozzles (Laval nozzles) have found broad application in industry and are used for accelerating gas streams from subsonic speed to supersonic speed.
One or a multiplicity of supersonic nozzles can be mounted at the periphery of the reactor.
The nozzles can be arranged in one or more planes.
The distance between the nozzles and the gas distributor plate is preferably at least 100 mm, particularly preferably 250 to 600 mm.
The Laval nozzles are preferably installed in such a manner that they terminate at, or are recessed from, the reactor inner wall.
The inclination of the nozzles to the horizontal is preferably less than 20xc2x0, particularly preferably 0xc2x0.
The supersonic nozzles are preferably arranged radially or at an angle to the radius.
The dimensions of the narrowest cross section and of the outlet cross section of the Laval nozzles depend upon the amount to be injected, the temperature and the Mach number of the reactants exiting from the nozzle and the available pressure of the components.
The nozzles are designed in accordance with the formulae for Laval nozzles known to those skilled in the art.
The invention further relates to a process for carrying out reactions in fluidized particle beds by passing a fluidizing gas through a gas distributor plate to produce the fluidized particle bed and by passing transversally one or more reactants into the fluidized particle bed, which comprises passing in the reactants by transversal injection at supersonic speed through supersonic nozzles.
The exit velocity of the reactants from the supersonic nozzle(s) is preferably at least Mach 1, particularly preferably at least Mach 1.5. The exit velocity is particularly preferably less than Mach 3.
The injected reactants can be gaseous. If the reactants are liquid or solid, they are injected into the fluidized particle bed by a carrier gas. Different reactants can be injected by separate nozzles.
The reactants which can be fed into the FPB by transversal supersonic injection are preferably gases, such as O2, H2, Cl2, hydrocarbons, steam and many others. However, liquids, such as fuel oil, atomized in a gas stream (carrier gas) or solids, such as coal dust, suspended in a gas stream can also be injected by the transversal supersonic nozzles.
The reactant injected can particularly preferably be pure oxygen or oxygen-enriched air, preferably containing at least 30% by volume of O2.
According to the invention, apart from the oxygen, in addition, combustible reactants can be fed to the fluidized bed through separate nozzles by transversal injection at supersonic speed.
Blowing in oxygen and, if appropriate, combustible reactants transversally at supersonic speed increases the mixing energy in the fluidized particle bed and thus improves the radial heat and mass transport. This results in a uniform box-like temperature profile and a homogeneous mass distribution, which leads to a uniform product quality. The additional supply of oxygen makes possible a considerable increase in the throughput at a given inlet area, or a decrease in the inlet area when a new fluidized-bed reactor is built.
The process described of transversal supersonic injection of oxygen and, if appropriate, combustible reactants, may be used advantageously with all oxidation processes in fluidized beds, for example in the oxidizing roasting of sulfidic ores or the gasification of coal, in the thermal cracking of waste sulfuric acids, salts, pickling baths and caustic baths, in the calcination of alumina, the combustion of sewage sludges or wastes, in the recycling of waste foundry sands, in the regeneration of catalysts and in the cracking of hydrochloric acid. The process according to the invention in this case is not restricted to the processes which are listed above and are mentioned only by way of example.
The apparatus according to the invention and the process according to the invention offer advantages, particularly, if the fluidizing gas and a further reactant are not to come into contact with one another until in the FPB, as is the case, for example, with calcination processes. In this case, air is used for fluidizing and a fuel is burnt in the FPB. Hitherto, this process has required complicated gas distributor plates in order to introduce the air and the fuel separately through the gas distributor plates through a multiplicity of orifices/nozzles. The process according to the invention here then makes it possible to feed in fuel through relatively few transversal supersonic nozzles and to introduce the fluidizing air through a simple gas distributor plate having a small cross section, the operating temperature of the gas distributor plate being below that of the prior art. Feeding fuel into the FPB at ultrasonic speed produces an excellent radial mixing of fuel, fluidizing air and fluidized particles. By means of additional supersonic injection of oxygen, in addition, a considerable increase in capacity can be achieved for a given reactor.
Processes for which particular advantages are achievedxe2x80x94as described abovexe2x80x94by transversal supersonic injection of fuels and, if appropriate, oxygen, which may be mentioned are, in addition to the calcination processes, for example, the oxidizing thermal treatment of ores, the deoiling of millscales and others, the combustion of sewage sludge or refuse, the partial or complete reduction of ores, the thermal cracking of metal chlorides or metal sulfates, the oxidizing roasting of sulfidic ores etc.
The process according to the invention and the reactor according to the invention also offer advantages in the preparation of chlorides of titanium, silicon, zirconium and other metals, in which the gas distributor plates are exposed to a particularly high chemical attack. The gas distributor plates may be kept relatively small, for example.
Advantageously, the invention may also be employed in the case of fluidized-bed heat-treatment furnaces, in which N2 or carburizing agents such as natural gas, methanol or CO can be injected through the Laval nozzles.
Further processes in which the inventions have advantageous effects are cracking processes, hydrogenation reactions, processes for regenerating catalysts, in particular processes for burning off carbon deposits and others. The processes in which the reactors according to the invention and the process according to the invention offer advantages are listed by way of example, and the list is not restricted to these processes.